Chemical functionality of interfacial water enveloping nanoscale structural defects in proteins

Building upon a non-Debye multiscale treatment of water dielectrics, this work reveals the biochemical role of interfacial water enveloping nanoscale structural defects in soluble proteins, asserting its role as a chemical base. This quasi-reactant status is already implied by the significant concentration of structural defects in the vicinity of an enzymatically active site, delineating their role as promoters or enhancers of catalytic activity.Fil: Fernandez, Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Argentino de Matemática; Argentin

Effects of Irradiation Temperature and Dose Rate on the Mechanical Properties of Self-Ion Implanted Fe and Fe-Cr Alloys

Pure Fe and model Fe-Cr alloys containing 5, 10 and 14%Cr were irradiated with Fe+ ions at a maximum energy of 2MeV to the same dose of 0.6dpa at temperatures of 300 C, 400 C and 500 C, and at dose rates corresponding to 6 x 10-4 dpa/s and 3 x 10-5 dpa/s. All materials exhibited an increase in hardness after irradiation at 300 C. After irradiation at 400 C, hardening was observed only in Fe-Cr alloys, and not in the pure Fe. After irradiation at 500 C, no hardening was observed in any of the materials tested. For irradiations at both 300 C and 400 C, greater hardening was found in the Fe-Cr alloys irradiated at the lower dose rate. Transmission electron microscopy and atom probe tomography of Fe 5%Cr identified larger dislocation loop densities and sizes in the alloy irradiated with the high dose rate and Cr precipitation in the alloy irradiated with the low dose rate.Comment: 42 pages, 6 figure

CBS domains form energy-sensing modules whose binding of adenosine ligands is disrupted by disease mutations

CBS domains are defined as sequence motifs that occur in several different proteins in all kingdoms of life. Although thought to be regulatory, their exact functions have been unknown. However, their importance was underlined by findings that mutations in conserved residues within them cause a variety of human hereditary diseases, including (with the gene mutated in parentheses): Wolff-Parkinson-White syndrome (γ2 subunit of AMP-activated protein kinase); retinitis pigmentosa (IMP dehydrogenase-1); congenital myotonia, idiopathic generalized epilepsy, hypercalciuric nephrolithiasis, and classic Bartter syndrome (CLC chloride channel family members); and homocystinuria (cystathionine β-synthase). AMP-activated protein kinase is a sensor of cellular energy status that is activated by AMP and inhibited by ATP, but the location of the regulatory nucleotide-binding sites (which are prime targets for drugs to treat obesity and diabetes) was not characterized. We now show that tandem pairs of CBS domains from AMP-activated protein kinase, IMP dehydrogenase-2, the chloride channel CLC2, and cystathionine β-synthase bind AMP, ATP, or S-adenosyl methionine,while mutations that cause hereditary diseases impair this binding. This shows that tandem pairs of CBS domains act, in most cases, as sensors of cellular energy status and, as such, represent a newly identified class of binding domain for adenosine derivatives

Exploring the equivalence of two common mixture models for duration data

The beta-geometric (BG) distribution and the Pareto distribution of the second kind (P(II)) are two basic models for duration-time data that share some underlying characteristics (i.e., continuous mixtures of memoryless distributions), but differ in two important respects: first, the BG is the natural model to use when the event of interest occurs in discrete time, while the P(II) is the right choice for a continuous-time setting. Second, the underlying mixing distributions (the beta and gamma for the BG and P(II), respectively, are very different—and often believed to be non-comparable with each other. Despite these and other key differences, the two models are strikingly similar in terms of their fit and predictive performance as well as their parameter estimates. We explore this equivalence, both empirically and analytically, and discuss the implications from both a substantive and methodological standpoint

A semi-classical over-barrier model for charge exchange between highly charged ions and one-optical electron atoms

Absolute total cross sections for electron capture between slow, highly charged ions and alkali targets have been recently measured. It is found that these cross sections follow a scaling law with the projectile charge which is different from the one previously proposed basing on a classical over-barrier model (OBM) and verified using rare gases and molecules as targets. In this paper we develop a "semi-classical" (i.e. including some quantal features) OBM attempting to recover experimental results. The method is then applied to ion-hydrogen collisions and compared with the result of a sophisticated quantum-mechanical calculation. In the former case the accordance is very good, while in the latter one no so satisfactory results are found. A qualitative explanation for the discrepancies is attempted.Comment: RevTeX, uses epsf; 6 pages text + 3 EPS figures Journal of Physics B (scehduled March 2000). This revision corrects fig.

Hepatitis A seroprevalence in Western Cape Province South Africa: Are we in epidemiological transition

Background. Hepatitis A virus (HAV) is the most common cause of viral hepatitis worldwide. Hepatitis A vaccine is not included in the Expanded Programme on Immunisation in South Africa (EPI-SA), as the country is considered to be highly endemic for hepatitis A.Objectives. To determine the seroprevalence of hepatitis A infection in Western Cape Province (WCP), South Africa.Methods. We conducted a cross-sectional seroprevalence study in the 1 - 7-year age group in WCP. Our samples (N=482) were blood specimens left over after laboratory testing obtained from referral hospitals between August and October 2015. A Siemens enzyme immunoassay was used to test for total hepatitis A antibodies. We also analysed hepatitis A immunoglobulin G antibody results from the National Health Laboratory Service (NHLS) Disa*Lab database at Groote Schuur Hospital from 2009 to 2014, and included 2009 - 2014 acute hepatitis A (immunoglobulin M-positive) surveillance data from the National Institute for Communicable Diseases to look at trends in notified acute infections over the same period.Results. Our cross-sectional study showed 44.1% seroprevalence in the 1 - 7-year age group. Hepatitis A data from the NHLS database indicated a seroprevalence of <90% up to age 10 years, indicating intermediate endemicity. The surveillance data showed that a substantial number of symptomatic hepatitis A infections occurred in the 7 - 40-year age group, suggesting that an increasing proportion of the population is susceptible to HAV infection.Conclusions. These results suggest an urgent need for detailed evidence-based considerations to introduce hepatitis A vaccine into the EPI-SA

Hepatitis A seroprevalence in Western Cape Province, South Africa: Are we in epidemiological transition?

Background. Hepatitis A virus (HAV) is the most common cause of viral hepatitis worldwide. Hepatitis A vaccine is not included in the Expanded Programme on Immunisation in South Africa (EPI-SA), as the country is considered to be highly endemic for hepatitis A.Objectives. To determine the seroprevalence of hepatitis A infection in Western Cape Province (WCP), South Africa.Methods. We conducted a cross-sectional seroprevalence study in the 1 - 7-year age group in WCP. Our samples (N=482) were blood specimens left over after laboratory testing obtained from referral hospitals between August and October 2015. A Siemens enzyme immunoassay was used to test for total hepatitis A antibodies. We also analysed hepatitis A immunoglobulin G antibody results from the National Health Laboratory Service (NHLS) Disa*Lab database at Groote Schuur Hospital from 2009 to 2014, and included 2009 - 2014 acute hepatitis A (immunoglobulin M-positive) surveillance data from the National Institute for Communicable Diseases to look at trends in notified acute infections over the same period.Results. Our cross-sectional study showed 44.1% seroprevalence in the 1 - 7-year age group. Hepatitis A data from the NHLS database indicated a seroprevalence of <90% up to age 10 years, indicating intermediate endemicity. The surveillance data showed that a substantial number of symptomatic hepatitis A infections occurred in the 7 - 40-year age group, suggesting that an increasing proportion of the population is susceptible to HAV infection.Conclusions. These results suggest an urgent need for detailed evidence-based considerations to introduce hepatitis A vaccine into the EPI-SA